Descriptions in antiquity of the execution cross, whether by Christians or non-Christians, present the instrument ordinarily used in putting people to death by crucifixion as composed of two wooden pieces. Whether the two pieces of timber of the normal execution cross were permanently conjoined or were merely put together for the purpose of the execution is not stated.
Atypical executions on cross-like structures also took place, "especially when the executioners decide[d] to engage in cruel creativity", as indicated by Seneca the Younger.
Terminology
A distinction is commonly made between a single-pole or single-stake crux simplex and a crux compacta composed of more than one piece of timber. This terminology was invented by Justus Lipsius (1547–1606) and so was not used by the Early Christians or their contemporaries.
Lipsius distinguished two types of the transom-less crux simplex: the crux simplex ad affixionem to which the victim was attached and left to die, and the crux simplex ad infixionem with which to impale him. Similarly, he distinguished three types of crux compacta: crux decussata (X-shaped), crux commissa (T-shaped) and crux immissa (†-shaped).
Some scholars think the distinction between crux commissa and crux immissa within the crux compacta category is unnecessary. Hermann Fulda called it a meaningless distinction that Lipsius grabbed out of thin air. Others too, including Gerald G. O'Collins, do not accept all the proposed subcategories of crux compacta.
Seneca the Younger (c. 4 BC – AD 65) records the use in the first century AD of the crux compacta with transom (patibulum) and of the crux simplex ad infixionem (impalement), but does not mention the transom-less crux simplex ad affixionem; he seems to indicate that execution on a cross tended to follow a fairly common routine, while still being open to significant variations.
Departure from normal crucifixion routine is also mentioned by Josephus (37 – c. 100) in his The Jewish War: "The soldiers, out of the wrath and hatred they bore the Jews, nailed those they caught, one after one way, and another after another, to the crosses, by way of jest, when their multitude was so great, that room was wanting for the crosses, and crosses wanting for the bodies".
Made of more than one piece
Irenaeus (early 2nd century – AD 202) remarks that "the very form of the cross, too, has five extremities, two in length, two in breadth, and one in the middle, on which [last] the person rests who is fixed by the nails".
The same remark is made by Justin Martyr (100–165) when commenting on the Book of Deuteronomy 33:17: "No one could say or prove that the horns of a unicorn represent any other fact or figure than the type which portrays the cross. For the one beam is placed upright, from which the highest extremity is raised up into a horn, when the other beam is fitted on to it, and the ends appear on both sides as horns joined on to the one horn. And the part which is fixed in the centre, on which are suspended those who are crucified, also stands out like a horn; and it also looks like a horn conjoined and fixed with the other horns".
To the pagan jibe about Christians being devotees of the cross, Tertullian (c. 155 – c. 240) responds by saying the pagans no less adored images of wood, with the difference that they worship what is only part of a cross, while the Christians are credited with "an entire cross complete with a transverse beam and a projecting seat". He then adds that "the very structure of our body suggests the essential and primal outline of a cross. The head ascends to the peak, the spine stands upright, the shoulders traverse the spine. If you position a man with his arms outstretched, you shall have created the image of a cross."
Justin Martyr also states: "That [passover] lamb which was commanded to be wholly roasted was a symbol of the suffering of the cross which Christ would undergo. For the lamb, which is roasted, is roasted and dressed up in the form of the cross. For one spit is transfixed right through from the lower parts up to the head, and one across the back, to which are attached the legs of the lamb."